Hello rocketeers!
A little story first. As part of a community (hashtagmars), a discussion about amateur space exploration and a crowd-sourced based project came up. An inspiration was amongst others Planet Labs and Local Motors. That discussion then directed itself to "budget" launch capabilties and rockoons. We understand that there are some issues with launching rockoons (ignition at high altitude, no aerodynamic stabilisation, stability of the launch platform,...) but they seem to be all elements that can be overcome. I've actually read the numerous threads of the topic in this forum: extremely informative. Obviously our discussion is purely theoretical at this point.
I wanted to do a quick dimensioning a feasibility test so I went over to our trusty Excel (disclaimer: I know there are dedicated programs, Rocksim, SpaceCade and OpenRocket, but they seem to resist me when simulating a rockoon).
Here is what I did in Excel:
We suppose a sounding rocket, launching at 30km altitude (burst of the baloon). We want to reach the mythical 100km.
The dry mass was estimated at 7kg and the drag was supposed to be negligible at these altitudes.
I used sugar candy as a propellant and supposed an Isp of 120s. So from 30km to 100km -> 70km = m*g*h = 4807 kj (g is supposed to be constant) The delta v needed can hence be calculated by the kinetic energy formula: sqrt (4807000*2/7) = 1171 m/s
You can then modify the formula for specific impulse and get that Delta V = ln (Mwet/Mdry)*Isp*9,81
That gives you fuelmass = 7*exp(1171/(120*9,81))-7 = +- 12kg.
Have I done anything wrong? How would you go forward from there? How would you account for the fuel burnt? Any other way than through infinitesimal steps? Thanks for your help!
A little story first. As part of a community (hashtagmars), a discussion about amateur space exploration and a crowd-sourced based project came up. An inspiration was amongst others Planet Labs and Local Motors. That discussion then directed itself to "budget" launch capabilties and rockoons. We understand that there are some issues with launching rockoons (ignition at high altitude, no aerodynamic stabilisation, stability of the launch platform,...) but they seem to be all elements that can be overcome. I've actually read the numerous threads of the topic in this forum: extremely informative. Obviously our discussion is purely theoretical at this point.
I wanted to do a quick dimensioning a feasibility test so I went over to our trusty Excel (disclaimer: I know there are dedicated programs, Rocksim, SpaceCade and OpenRocket, but they seem to resist me when simulating a rockoon).
Here is what I did in Excel:
We suppose a sounding rocket, launching at 30km altitude (burst of the baloon). We want to reach the mythical 100km.
The dry mass was estimated at 7kg and the drag was supposed to be negligible at these altitudes.
I used sugar candy as a propellant and supposed an Isp of 120s. So from 30km to 100km -> 70km = m*g*h = 4807 kj (g is supposed to be constant) The delta v needed can hence be calculated by the kinetic energy formula: sqrt (4807000*2/7) = 1171 m/s
You can then modify the formula for specific impulse and get that Delta V = ln (Mwet/Mdry)*Isp*9,81
That gives you fuelmass = 7*exp(1171/(120*9,81))-7 = +- 12kg.
Have I done anything wrong? How would you go forward from there? How would you account for the fuel burnt? Any other way than through infinitesimal steps? Thanks for your help!
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